Such a combination as described above, is known in practice and described, for instance, in U.S. Pat. No. 4,861,520, which is herewith incorporated by reference.
For local radioactive radiation treatment of a specific internal area of the human body, such as a tumor, or a wall section of a blood vessel, it is possible, as described in U.S. Pat. No. 4,861,520, to deliver a capsule with a radioactive source, via a tubular guiding device, such as, for instance, a hollow needle, a flexible tube or a catheter or the like, to the area to be treated. For this purpose, normally the so-called "after loading" technique is employed. First, the catheter or the like is placed in the body and then the capsule attached to the distal end of a guidewire is delivered with the help of a remotely controlled device to the treatment area (referred to as brachytherapy).
In order to deliver the capsule to the area to be treated in a reliable and safe manner via the tubular guiding device, even when the tubular guiding device is forming sharp curves, the capsule should be as short as possible and its front have a smooth shape without sharp transitions.
In the combination known from U.S. Pat. No. 4,861,520, the capsule has at the front, that is to say the end facing away from the guidewire, a closed, almost semi-spherical solid end that forms a whole together with the cylindrical mantle of the capsule. At the end facing the guidewire, the connection between the capsule and the guidewire is formed by a connecting device (coupling element), partly extending in the cylindrical mantle and connected through welding to the distal end of the guidewire and the cylindrical mantle. This makes possible a considerably shorter capsule with regard to the prior art, according to which the cylindrical mantle was provided at the front with a solid plug extending partly in the cylindrical mantle with a semi-spherical end. The obtained length advantage was on the order of 25% with the application of seven miniature radioactive source elements. With a conventional capsule with an original length of 7.2 mm and a diameter of 1.1 mm, a length reduction to a length of 5.5 mm was realized.
A problem with the known combination is that the wall thickness of the capsule in front at the place of the semispherical end is greater than that at the place of the cylindrical mantle. Thus, the capsule is still longer than necessary. Moreover, the greater wall thickness in the distal end of the capsule disturbs the radiation pattern, since, viewed from the source, more radiation is absorbed in the axial direction than in the radial direction.